We never knew it at the time, but it now appears certain that in January of 1961 — just three days after President John F. Kennedy was inaugurated — the United States barely escaped a nuclear disaster of unprecedented proportions when two hydrogen bombs were accidentally dropped near Goldsboro, North Carolina.

The B-52 aircraft carrying them broke apart in mid-air and the bombs, 260 times more powerful than the atom bombs that destroyed Hiroshima in 1945, fell to the ground.

Nuclear experts have estimated that had either bomb exploded the lethal fallout could have spread as far as Washington, Baltimore, Philadelphia and New York City, endangering thousands, if not millions, of lives. The bombs’ payload represented the equivalent of four million tons of TNT.

Fortunately, a low-voltage switch functioned properly and it appears that is the only thing that prevented the devastating explosion when the bombs struck the ground.

How do we know this after all these years? Because, over the weekend, The Guardian, the London newspaper that is more and more a source of significant international news (for example, it broke the story of Edward Snowden, the American security contractor who leaked so many classified documents), published in declassified form a secret government document that described the 1961 incident.

At the time of the incident, there had been considerable public speculation about how narrow the Goldsboro escape was, although the government repeatedly denied that any American lives were in jeopardy.

However, the newly-published document quotes a senior engineer in the Sandia National Laboratories (which are managed by Lockheed Martin on behalf of the defense department and are responsible for the mechanical safety of nuclear weapons) that “one simple, dynamo-technology, low voltage switch stood between the United States and a major catastrophe.”

Eight years after the incident, the Sandia scientist, Parker F. Jones, authored a document he called “Goldsboro Revisited or: How I Learned to Mistrust the H-bomb” and in it he stated conclusively that “one simple, dynamo-technology, low-voltage switch stood between the United States and a major catastrophe.”

The MK 39 Mod 2 bomb did not possess adequate safety for the airborne alert role in the B-52, he added.

“Jones found that of the four safety mechanisms in the Faro (the small town near Goldsboro where the bombs actually fell), designed to prevent unintended detonation, three failed to operate properly,” The Guardian reported. “When the bomb hit the ground, a firing signal was sent to the nuclear core of the device, and it was only that final, highly vulnerable switch that averted calamity.”

According to The Christian Science Monitor, which also reported on the matter this past weekend, the two bombs landed in a field and a meadow, near Faro, N.C., where there’s now a roadside marker commemorating the “nuclear mishap.” A spokesman for the Pentagon once insisted to a wire service reporter that the bombs were, in fact, unarmed and could not have exploded.

There have been similar near-misses. Three years before the near-disaster in rural North Carolina, a 7,600 pound Mark 15 nuclear bomb disappeared in Wassaw Sound, near Tybee Island, Ga., after a bomber and a fighter jet, both on training missions, collided. The bomb has never been found, and — the Christian Science Monitor adds — “arguments continue to this day about whether the lost Tybee Island nuke was armed.”

This all occurred during the Cold War, when the United States and the Soviet Union each believed the nuclear threat was genuine.

In that political climate, one can only imagine the consequences had there actually been an explosion.